1. It is acceptable to "call" what's going to happen next. It makes you cool if you're right, and a moron if you're not.
2. It is not acceptable to say "Oh, pay attention to this part!" when watching a movie with a first time viewer.
3. It is not acceptable to pre-laugh when watching a movie with a first time viewer.
4. It is acceptable to pre-laugh when all viewers have seen the movie before. In fact, this is encouraged.
5. It is not acceptable to ridicule what could/could not happen in action movies. Duh.
6. It is acceptable to point out attractive actors/actresses. But only once. Unless it's Johnny Depp.
7. It is acceptable to stop a movie in order to check IMDB so you can figure out where you've seen specific actors before. Otherwise, you'll miss parts of the movie while your brain is wandering.
Feel free to add some of yours ... but these are my rules.